For cultivation of a microorganism, there are heretofore known liquid culture and solid culture using rice bran, etc. These techniques are used alone or in combination, depending upon, e.g., kind of cells, metabolites, etc.
In a liquid culture, however, proliferation of pellets occurs during cultivation so that the cultivation efficiency of the microorganism decreases. Further, in a solid culture, it is difficult to isolate the product produced depending on microorganism used. Both culture techniques are disadvantageous in these regards.
In order to eliminate such drawbacks, there is proposed a method for cultivation by carrying medium components on a foam. For example, in Japanese Published Examined Patent Application No. 55-36313, a technique is shown which comprises impregnating a foam such as sponge, etc. with medium components and then performing a stationary culture. According to this technique, however, there is a limit in the amounts of the medium components to be impregnated. An impregnation rate is approximately 30 to 50 wt % with, e.g., commercially available polyurethane foam and about 90 wt %, even with a foam having a good impregnation property. Accordingly, a medium satisfactory for cultivation of a microorganism is not formed and effective cultivation is made only with difficulty. In addition, such a foam is extremely readily dried so that the foam is not always a good material to use for cultivation of a microorganism.
On the other hand, various techniques are proposed for liquid culture; for example, a method which comprises incorporating a large number of foam pieces (Japanese Published Unexamined Patent Application No. 60-214878), a method which comprises using a hydrophilic foam having formed a peptide matrix in the molecule thereof (Japanese Published Examined Patent Application No. 53-11316), a method which comprises using a foam for cultivating a microorganism, in a matrix of which foam medium components are contained (Japanese Published Unexamined Patent Application No. 63-74479), etc.
In these foams, however, the microorganism is cultured only on the surface of each foam so that the ratio of surface area to apparent volume is small, showing the tendency of a decrease in cultivation efficiency. Furthermore, since it is difficult to incorporate medium components only into the surface of foam, amounts of medium components more than required are necessary and such is disadvantageous from an economical viewpoint. Moreover, it is necessary to perform a sterilization treatment thereby to prevent contamination of the aforesaid foam with other bacteria until the foam is provided for use; however, at heat sterilization above 100.degree. C., the foam itself is denatured so that costly steam sterilization or gas sterilization is required.
On the other hand, molds such as Beauveria tenella, etc. are present as a natural enemy of longicorn beetles, gold beetles, whiteflies, rice insects, leafhoppers, etc. which damage various agricultural crops or trees. Using these natural enemy molds, various methods for terminating vermin have been proposed.
For example, Japanese Published Examined Patent Application No. 63-403 discloses a method which comprises directly sprinkling bacteria cultured in bran medium over trees together with medium. According to this method, however, the bacteria cannot utilize medium components sufficiently, but the bacteria are in a state such that they are close to dormant cells. Accordingly, an expected insecticidal effect is not exhibited sometimes. In addition, the method for extermination relies on sprinkling so that the bacteria adhere to trees only with difficulty, resulting in a poor insecticidal efficiency.
In order to solve these defects, Japanese Published Unexamined Patent Application No. 63-19080 proposes an elastic carrier such as a foam having cultured therein bacteria for infection. While the above defects are solved, however, the bacteria are not sufficiently closely adhered to the amorphous surface of trees, etc., even though they are disposed onto the surface thereof. Thus, the problem still remains unsolved. Where cardboard or the like is used as a carrier, it is preferred in view of natural degradation but has a poor mechanical strength so that a problem of breakage during use is involved.
The present invention has been made to solve the problems of the prior art described above and an object is to provide a culture carrier for cultivating microorganisms which can effectively incubate the microorganism.
Another object of the present invention is to provide a vermin exterminating element using the carrier described above.
A further object of the present invention is to provide a method for terminating vermin using the vermin exterminating element described above.